I had the problem when loading my Hack Mac that the wi-fi card always grabbed onto en0 and my built in ethernet always defaulted to en1. This cause all kinds of problems with using Apple's internet based services like the App Store, Facetime, and iCloud. These services require your built in ethernet port to be en0. To make the swap I had to go in and delete the following 2 files.
After you delete the two files reboot your computer and it should automatically regenerate them with en0 being correct. That's pretty much it.